1. Field of the Invention
The present invention relates to image processing. More particularly, the present invention relates to low resolution processing with high resolution printing.
2. Present State of the Art
Reproducing an image can be a difficult and costly process because many printers and printing devices and other output devices do not have the capability to produce continuous tone reproductions of images. Instead, the images which are reproduced in posters, magazines, newspapers and other products are created using a halftoning process which places tiny dots of ink in close proximity to one another. Because the dots of ink are small and close together, the human eye effectively sees continuous color.
Halftoning creates an illusion of continuous color and by varying the quantity of different inks which make up the image, a large number of different colors can be created. For instance, the main difference between black and gray in a halftone image is the number of tiny black ink dots placed on the printed product. By placing fewer dots on, for example, a white paper, the human eye effectively blends the whiteness of the paper with the tiny black dots to produce a shade of gray.
One of the primary color schemes employed in image reproduction uses cyan, magenta, yellow and black xe2x80x9cCMYKxe2x80x9d to produce color prints or reproductions. Each of these four colors is printed such that the desired colors and shades of colors of the original image are reproduced in the printed image and perceived by the human eye. In CMYK color schemes, a separate halftone image is created for each color and each halftone image is separately printed as the original image is being rendered on a medium. Each of the four halftone images is essentially printed on top of the other halftone images and the mixture of these colors produces the desired image. The separate colors are not printed directly on top of each other because the black dots of ink would effectively mask or block the cyan, magenta and yellow dots of ink. Rather, the dots are arranged in configurations, such as a rosette, well known in the prior art.
The amount and placement of the dots also has an affect on the resolution or sharpness of the image being reproduced. The human eye effectively blends halftone dots having densities of approximately 150 dots per inch (dpi). As technology has progressed, resolutions having halftone dot densities on the order of 1440 dpi and higher are possible. However, the resolution chosen for a particular image is usually dependent on the application and the cost. Newspapers, for example, typically employ lower resolutions while some posters are rendered at very high resolutions.
The ability to render an image at high resolutions comes at a cost. High resolution images require a substantial amount of memory to store the image and require a significant amount of time to process the image. These costs are incurred because a higher resolution necessarily has more dots to be printed or placed and each dot is typically processed for each color in the color scheme being used. For instance, a continuous tone image which is going to be reproduced is frequently an RGB (red, green and blue) image. In this image, 8 bits are used to describe the red portion, 8 bits to describe the green portion and 8 bits to describe the blue portion. The original image uses 24 bits to describe each pixel of the image. During processing of the image, the RGB color scheme is typically converted to the CMYK color scheme and the image is cropped and sized before the image is ready to be reproduced by a printer.
A significant problem is that while an image can be represented using a large number of bits for each pixel, the device which ultimately renders the reproduced image is typically capable of being either on or off. In other words, a typical printer can either place a dot or not place a dot and only one bit is required to perform this particular function. At the same time, representing an image with one bit per pixel is simply not an adequate method for reproducing an image. As a consequence, an image which is to be printed at a high resolution simply requires a lot of memory and time to reproduce the image.
It would be a significant advance in the art to be able to be able to render or reproduce an image with high resolution while reducing the memory and time requirements associated with the reproduced image.
It is an object of one embodiment of the present invention to render an image at higher resolutions while processing the image at lower resolutions.
It is another object of one embodiment of the present invention to reproduce an image using levels.
It is a further object of one embodiment of the present invention to reduce the memory required to reproduce an image.
It is another object of one embodiment of the present invention to reduce the time required to process an image which is being reproduced.
It is yet another object of one embodiment of the present invention to create a data structure for storing the dot placements of various levels.
It is a further object of one embodiment of the present invention to render a plurality of pixels simultaneously.
It is another object of one embodiment of the present invention to represent the output file of a processed image in levels.
The present invention provides for reproducing an image using less memory and less processing time without sacrificing significant resolution. In one embodiment, an original image is partitioned into pixels. The pixel size may vary, but is usually a fixed size for a particular image, and each pixel is comprised of a plurality of dots. Each dot is representative of an ink dot. After the image has been divided into pixels, each pixel is processed to determine a level. The level of the pixel is related to the quantity of ink that will be used to reproduce that pixel.
After a level has been assigned or associated with the pixels, all potential levels are stored in a data structure. The data structure contains the dot placement for all potential levels of ink. When a particular pixel is to be printed or reproduced, the data structure is accessed according to the level of the pixel being reproduced and the dot placement is reproduced by the printing or other output device on some medium. The dot placement is randomized to avoid undesirable effects in the reproduced image such as a moire effect.
In another embodiment, the levels generated by the processing may be used to cause a particular printer head to fire multiple times. The ability to fire or not fire a printer head a variable number of times permits various levels of ink to be placed on the medium receiving the ink dots. In another embodiment, the output device may have multiple heads of a single color and the level determines which of those heads will fire for a given level. This also permits varying quantities of ink to be placed on a medium. In this manner, the image is reproduced according to the levels assigned to the pixels. In yet another embodiment, the levels can represent the size of the ink dot to be rendered.
Depending on the desired resolution of the processed image, a plurality of pixels can be represented and rendered simultaneously. For instance, a byte can be divided into four pairs of bits. Each pair of bits is capable of representing four distinct outputs for four separate pixels. Thus, four pixels are simultaneously processed in this embodiment.
Additional objects and advantages of the present invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by the practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instruments and combinations particularly pointed out in the appended claims. These and other objects and features of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.